thunderstorms and severe weather
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What are the characteristics of a thunderstorm?
- cumulonimbus cloud with lightning and thunder
- often heavy rain and gusty winds
- some have hail or tornadoes
- average cell - 15 mi in diameter lasting 30 min
- multicell clusters are most common
What characterizes a severe thunderstorm?
- wind > 58 mph
- hail > 3/4 inch
- generates a tornado
What conditions cause a severe thunderstorm?
- daily heating
- squall line from a front
- sea breeze convergence
- outflow boundary
What are the hazards associated with thunderstorms?
How much lightning is cloud to cloud?
How hot can lightning be?
54,000 degrees F (air)
How many get killed in the US every year by lightning/injured?
- kills 100 per year
- injures 300 per year
How does lightning form?
- large electrical charge imbalance
- upper cloud has + charge
- lower cloud has - charge
- charge is induced below thunderstorm on ground
- stepped leader of ionized air branches downward
- spark jumps from tall object to stepped leader
- flowing electrons create return stroke
What do you do and what do you avoid when caught outside in a thunderstorm with lightning?
- avoid contact with metal
- take cover if at an outdoor event
- don't be the tallest point around
- don't huddle with other people, spread out
How are buildings protected from lightning strikes?
lightning rods thanks to Ben Franklin
How can lightning kill you indoors?
- on a corded, landline telephone
- typing on a desktop computer
- taking a shower or bath
- near an open window, opening, or on the porch
How is risk from thunderstorms mitigated?
- forecasting: doppler radar
- predicting: watches and warnings
- construction: windproofing, community shelters
- personal actions: NOAA radio, prepared safe room
What are other hazards from weather and their risks?
- blizzards: extremely low visibility, wind chill effect and frostbite
- fog: extremely low visibility, smog and vog even worse
- ice storms: ice accumulates destroying utility lines and trees, travel not possible
- drought: crops fail, food shortages
- dust storms: widespread roof and tree damage, contribute to wildfires
- heat waves: heat stress, dehydration
How do humans exacerbate these weather hazards?
- urban heat island
- global warming
Mesoscale Convective System (MCS)
large, circular, long-lived and interacting group of thunderstorms
- squall line
- a line of thunderstorms
cellular pattern of pouches hanging underneath the base of a cloud
a channel of ionized air that approaches the earth in a series of nearly invisible bursts
natural hollow glass tubes formed in sand or soil when lightning strikes
- positively charged
- originates from top of cloud
- 3 to 100 times more powerful than regular lightning
last resort way of crouching if you are in lightning prone area
- take shelter when flash to bang is less than 30 seconds
- remain in safe place for 30 min after hearing last thunder
National Weather Service
a branch of NOAA that is responsible for weather forecast and preparation of weather maps
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